The rapid and sometimes ruthless gentrification of San Francisco threatens to kill the neighborhoods that made it The CityGavin Hellier/Corbis

Patricia Kerman was born in Detroit in 1949. That year, the Motor City's banks reported record-high deposits, unemployment dropped to its lowest level ever, and manufacturers churned out the automobiles, electric refrigerators, stoves and calculators that were fast defining modern life in the second half of the 20th century. It was, as The New York Times wrote in 1950, an "unprecedented industrial boom."

But for all its postwar prosperity, America's "Arsenal of Democracy," as President Franklin Roosevelt dubbed Detroit, was a violent place to live. The city was plagued by police brutality and race riots. Urban planners ripped out electric streetcars and destroyed public housing, evicting thousands for freeway expansion. Like many Midwesterners of her generation, when Kerman saw a way out, she took it: In the summer of 1969, after friends asked her to join them on a road trip to California, she told her parents she'd be back in 10 weeks, hopped in a van and never returned.